- The importance of having an a priori model to guide our imaginative thoughts and research is desirable in any discipline. This is particularly important in a slowly changing system under continuous development such as soils where the separation of cause and effect is most difficult. A model of soil development based on energy vectors operative in soils is presented and discussed. The model proposed is simple initially but can become as complex as the situation requires. The model proposed is simple initially but can become as complex as the situation requires. The model discussed may enable one to design experiments which have a higher probability of definitive results than do previous models. Also the model seems to allow for easier extrapolation of results. Hopefully the proposed model will help in predicting more accurately the effect of mans activity on soils of the world. 1973 The Williams & Wilkins Co.